Film coaters cannot use a leading well or reservoir. The leading element would scratch film. Therefore, they have a removable barrier or a small delivery system mounted to the top that can measure the emulsion as the coater moves. In the case of the barrier, the surface tension and viscosity of the emulsion holds it in place, but even without these devices, the coaters work but with more waste that runs off at the edges.
You place the coater at the top edge of the film (or plate) and pour emulsion in front of the leading edge. If you have a barrier, the emulsion does not spread out, but if you do not, the emulsion spreads out quickly so you have to be agile. You draw the blade towards you and leave behind a beautiful sheet of film.
The attachment shows a sheet of film for 4x5 format. Very high quality can be obtained by this method. Well, you have probably seen this photo before.
The coaters shown will not work with paper due to swell caused by the unrestrained spread of emulsion without a well or leading weight.
They are all hand operated devices.